The present document is based on Japanese Priority Document JP 2001-327038, filed in the Japanese Patent Office on Oct. 25, 2001, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, which forms a conductive layer composed of a silicon film and the like on an oxide film formed as an insulating layer, by using a chemical vapor deposition (CVD) method, and more particularly relates to a method of manufacturing a semiconductor device, which avoids a drop in an dielectric breakdown resistance of an insulating layer and a reduction in a long-term reliability.
2. Description of Related Art
As a semiconductor device, for example, when a MOS type transistor is manufactured, it is necessary to form a source diffusion region, a drain diffusion region and a channel region on a main surface of a silicon substrate and at least form a gate insulating layer on the channel region. The gate insulating layer is usually composed of a silicon oxide film, a metal oxide film and the like.
Also, when a thin film transistor (TFT) is manufactured as a semiconductor device, it is necessary to form a gate insulating layer composed of a silicon oxide film on a surface of a silicon layer formed on an insulation substrate.
Since a gate electrode and the channel region are surely insulated by the gate insulating layer, it is not too much to say that the reliability of the semiconductor device is reserved.
For this reason, a high dielectric breakdown resistance and a long-term reliability are always required of the gate insulating layer composed of the silicon oxide film, the metal oxide film and the like.
By the way, a silicon gate type of a transistor is well known which has a gate electrode formed by depositing a silicon film on a gate insulating layer formed through oxidization reaction.
In the above-mentioned transistor, the silicon film is formed by the CVD method in many cases. In such a case, material gas, such as a monosilane (SiH4) gas and the like, is introduced into a CVD furnace where a temperature and a pressure satisfying a predetermined film formation condition are maintained. Then, in a high temperature atmosphere, the silicon film is deposited on the gate insulating layer.
However, even in the case of the inclusion of the gate insulating layer in which the high dielectric breakdown resistance can be obtained, if the silicon film is then deposited in the high temperature atmosphere of the SiH4 gas as mentioned above, there may possibly occur a problem as described below.
That is, as shown in FIG. 4, suppose that a silicon oxide film 42 which has silicon (Si) and oxygen (O) as constituent elements and has no defect is formed on a silicon wafer 40.
In this case, when a silicon film 44 (refer to FIG. 6) is deposited in the high temperature atmosphere, the silicon oxide film 42 is exposed to the SiH4 gas that is a so-called reducing gas. Thus, as shown in FIG. 5, when the oxygen contained in the gate insulating layer 42 as the constituent element is coupled to hydrogen (H) in the SiH4 gas, the oxygen is lost by the amount corresponding to the coupling from the gate insulating layer 42.
For this reason, as shown in FIG. 6, after the deposition of the silicon film 44, it becomes the silicon oxide film 42 having oxygen deficiency 46. Thus, this results in the drop in the dielectric breakdown resistance and the reduction in the long-term reliability of the gate insulating layer 42.
The present invention is proposed in view of the above-mentioned problems. Accordingly, the present invention provides a manufacturing method of manufacturing a semiconductor device, which while forming a conductive layer on an oxide film formed as an insulating layer by using the CVD method, protects the oxygen deficiency of the oxide film without any drop in the dielectric breakdown resistance as the insulating layer of the oxide film and without any reduction in the long-term reliability.
This invention aims at a fact that when the conductive layer is deposited by using the CVD method after the formation of the oxide film as the insulating layer, if the oxide film is not exposed to a reducing atmosphere, the problem of the deficiency of oxygen contained in the oxide film as the constitutent element of a compound can be solved. Then, the repetition of various experiments leads to the present invention.
The method of manufacturing the semiconductor device, according to the present invention, is characterized in that when the conductive film is formed on the oxide film formed as the insulating layer, the conductive film is formed in a non-reducing atmosphere.
In the method of manufacturing the semiconductor device according to the present invention, the conductive layer is not formed in the conventional reducing atmosphere but in the non-reducing atmosphere. Thus, oxygen contained in the oxide film as the constituent element of the compound is not lost when the conductive layer is formed. For this reason, the oxygen deficiency is not induced in the oxide film as the insulating layer. Hence, it is possible to obtain the semiconductor device without any drop in the dielectric breakdown resistance as the insulating layer and without any reduction in the long-term reliability.
For example, when the silicon film is formed as the conductive layer, a silicon material gas that does not contain hydrogen as the constituent element of the compound can be used as the material gas constituting the non-reducing atmosphere. In specific, the silicon material gas can be composed of silicon tetrachloride (SiCl4), disilicon hexachloride (Si2Cl6) or SixCl2x+2 (xxe2x89xa73) of a higher order.
Also, when a silicon germanium film is formed as the conductive layer, a germanium material gas and the silicon material gas that do not contain hydrogen as the constituent element of the compound can be used as the material gas constituting the non-reducing atmosphere. Specifically, the silicon material gas can be composed of SiCl4, Si2Cl6 or SixCl2x+2 (xxe2x89xa73) of a higher order, and the germanium material gas can be composed of germanium tetrachloride (GeCl4).
For example, the oxide film can be made of any of silicon dioxide (SiO2), hafnium dioxide (HfO2), alumina (Al2O3), zirconium dioxide (ZrO2), ditantalum pentaoxide (Ta2O5), praseodymium dioxide (PrO2), lanthanum oxide (LaOx), titanium dioxide (TiO2) and diniobium pentaoxide (Nb2O5).
Also, a phosphorus material gas and the silicon material gas that do not contain hydrogen as the constituent element of the compound are used as the material gas constituting the non-reducing atmosphere, and a phosphorus doped silicon film can be formed as the conductive layer.
Specifically, the silicon material gas can be composed of SiCl4, Si2Cl6 or SixCl2x+2 (xxe2x89xa73) of a higher order, and the phosphorus material gas can be composed of phosphorus trioxide (PCl3), phosphorus tri-bromide (PBr3), phosphorus pentachloride (PCl5) or phosphorus pentabromide (PBr5). Also, the oxide film can be made of any of SiO2, HfO2, Al2O3, ZrO2, Ta2O5, PrO2, LaOx, TiO2 and Nb2O5.
As mentioned above, according to the present invention, it is possible to obtain the semiconductor device, in which when the conductive film is formed on the oxide film formed as the insulating layer, the conductive film is formed in the non-reducing atmosphere, and while the conductive layer is formed on the oxide film by the CVD method and the like, the oxygen deficiency of the oxide film can be avoided without any drop in the dielectric breakdown resistance as the insulating layer of the oxide film and without any reduction in the long-term reliability.